MediaWiki:Mergehistory-fail-timestamps-overlap

This history merge operation cannot be performed because it would result in parallel histories (revisions of the source page and the destination page being mixed together).

The usual cause of this is error that the source page was a redirect before it was overwritten with a cut-paste, in which case you need to clear away the redirect before going forward with the merge. Otherwise, please make sure you have selected the correct set of revisions to merge and try again.

If you really really know what you are doing and want to combine overlapping chunks of revisions (even though it will result in diffs comparing two unrelated versions for example), then you can do it by doing multiple merges each of smaller chunks. But you almost certainly shouldn't.